Preliminary evidence shows that exposure to the carcinogen, styrene-7, 8-oxide (SO) which arises from reactions of styrene during the production of reinforced plastics and from metabolism of styrene, causes significant increases of SO biomarkers in workers. Biomarkers are the adducts of SO with DNA and serum albumin and sister chromatid exchanges. The proposed study is intended to determine the relative contributions of inhaled styrene and SO to the dose of SO in the blood of workers in the reinforced plastics industry. Part one of this project involves recruitment of 100 workers within 17 sites in the reinforced plastics industry. A measurement of airborne exposure of styrene and SO for each worker twice during one year will be done as well as collection of blood samples. This project is being submitted to the Committee for the Protection of the Rights of Human Subjects and the GCRC in order to complete one of the secondary objectives: to determine whether SO per se is the source of background adducts of SO in human blood by using ultratrace analyses of SO in the blood of 100 persons without occupational exposures to styrene or SO. Protein and DNA adducts will also be measured in these persons to allow comparison of background adduct levels with those of SO in the blood.